Exhausted primary and secondary batteries and cells face increasingly stringent rules regarding disposal. In particular, environmental regulations require the responsible handling and treatment of cadmium--a primary component in nickel-cadmium cells. Cadmium is a poison that wreaks havoc with living systems. Accordingly, various separating systems have been developed to recover and recycle cadmium and nickel from retired cells.
Nickel-cadmium cells and battery packs are typically contained in and/or are held together by polymeric or plastic materials. Cells include nickel, cadmium, paper, cardboard, water, electrolyte and assorted polymers. In order to separate the cadmium nickel and iron from the remaining materials, the cells are usually heated in controlled environments. Other processes utilize hydrometallurgy techniques for separation and recovery.
Typically, the polymers and other non-valuables are pretreated in static bed furnaces to heat the cells until the polymers are vaporized followed by the use of an after burner and rapid quenching to destroy any dioxin/furan compounds that may form prior to gas discharge to the atmosphere. This batch technique is substantially limited to the volume of the stationary furnace, requiring cycle times up to 24 hours. Heating is not uniform and it is difficult to control the temperature in a static bed where various exothermic reactions occur. Water has to be used to quench run-away reactions resulting in a wet product with incomplete plastic removal.
Recycling methods employing pyrometallurgical techniques generally shred the polymeric cell cases to free up the internal cell components. The crushed scrap is then heated in a furnace to vaporize the cadmium. The gaseous cadmium is condensed and is generally solidified as ingot, granules or other desired shapes. The residue, mainly consisting of nickel and iron, is subsequently treated to make a nickel-iron alloy pig.
U.S. Pat. No. 4,401,463 to Melin et al. discusses an involved batch pyrometallurgical process wherein the scrapped batteries are preheated prior to the pyrolysis of the cadmium. Vaporization of the cadmium occurs in the presence of an inert gas and a small quantity of oxygen. The non-continuous technique requires laboriously locomoting the treated batches through several stations prior to casting of the cadmium.
U.S. Pat. No. 5,437,705 to DeLisle et al. deposits the shredded innards of nickel-cadmium batteries in a furnace along with the addition of an oxygen getter, such as carbon, to prevent oxidation. An inert blanket gas, preferably argon, is used to maintain the reducing atmosphere in the furnace. Cadmium cubes and nickel-iron residue are produced.
U.S. Pat. No. 5,252,189 to Celi discloses a process for separating the metal and plastic components from mercury containing cells. The cells are fed into a slightly heated rotating ball mill where the tumbling action of the balls in conjunction with the low grade heat separates the components for subsequent treatment. Heated inert gas, such as nitrogen, is fed into the mill and is eventually washed with sulfuric acid to free up the mercury. The now separated plastic and metal residues are subsequently and independently treated.
In order to efficiently and economically recycle spent nickel-cadmium cells by recovering the cadmium and nickel, the plastic, water and paper must be eliminated. Raising the temperature of the various hydrocarbon polymeric packing material in combination with the contents of the cells past their auto ignition temperatures in a closed vessel such as a furnace strongly creates the possibility of an explosion and fire. Indeed, in the assignee's experience, the utilization of a large rotary calciner, ostensibly having an inert atmosphere, resulted in undesirable explosions and fires caused by the unintended entrainment of oxygen in the vessel.
Accordingly, there is a need for an apparatus and method to safely and efficiently remove polymeric components, water, and other non-metal values from battery packs and cells while minimizing the fuming of the noxious elements from the batteries.